A resonance apparatus is a scientific instrument used to explore the resonant behavior of an enclosed air column when it is stimulated by an external sound source. Specifically, it helps us investigate the resonance phenomenon in an open-ended cylindrical tube and determine the velocity of sound in air at ordinary temperatures.

Here’s how it works:

1. Setup:

   • The apparatus consists of a long cylindrical plastic tube attached to a water reservoir.
   • The length of the water column can be adjusted by raising or lowering the water level while a tuning fork is held over the open end of the tube.

2. Resonance Phenomenon:

   • Resonance occurs when the column length matches specific fractions of the sound wavelength (λ/4, 3λ/4, 5λ/4, etc.).
   • The water surface acts as a node of the standing wave since the air cannot move longitudinally.
   • The open end provides the conditions for an antinode, although the actual antinode occurs slightly outside the tube (about 0.6 times the tube radius from the end).

3. Procedure:

   • Fill the tube nearly full of water.
   • Strike a tuning fork and hold it above the water column (careful not to touch the tube with the rapidly moving fork).
   • Lower the water surface slowly, listening for amplification of the tone.
   • When resonance is found, a pronounced reinforcement of the sound will be heard.
   • Mark the point of maximum sound intensity with a rubber band on the outside of the tube.
   • Continue adjusting the water level to find the next resonant length (λ/4, 3λ/4, etc.).
   • Calculate the wavelength and velocity of sound using the measured lengths.
   • Repeat the procedure for other tuning forks.

4. Velocity Calculation:

   • The velocity of sound in air can be determined using the known frequency of the tuning fork and the resonance positions.
   • The velocity in meters per second (m/s) can be converted to miles per hour (mph) by multiplying by the factor 2.24.